Array of ZnO nanoparticle-sensitized ZnO nanorods for UV photodetection Zahra Alaie • Shahram Mohammad Nejad • Mohammad Hasan Yousefi Received: 9 August 2013 / Accepted: 29 November 2013 / Published online: 12 December 2013 Ó Springer Science+Business Media New York 2013 Abstract Vertically aligned ZnO nanorod (NR) arrays have been successfully synthesized on ITO-glass substrate by hydrothermal growth. Chemical bath deposition method was used to deposit ZnO nanoparticles (NPs) onto the ZnO NRs. These structures were applied in fabricating ZnO NPs sensitized ultraviolet (UV) photodetectors (PDs). Incorpo- ration of ZnO NPs onto ZnO NRs results in distinct improvement of optical properties of ZnO NRs, i.e., sig- nificant enhancement of emission as well as effective suppression of defects emission in ZnO. Furthermore, there is a noticeable blue-shift in absorption spectra compared with that of ZnO NRs structure. I–V characteristics show that the sensitized structure improved photocurrent almost twice that of unsensitized ZnO NRs. Consequently, these findings may open new opportunities for the integration of different ZnO nanostructures for application in UV region particularly fabrication of UV PDs. 1 Introduction Zinc oxide (ZnO) is a wide direct band gap n-type semi- conductor (3.37 eV) with a large exciton binding energy (60 meV) that makes it suitable for UV photodetection. One dimensional (1D) ZnO nanostructures have been shown the improved optical and electrical properties due to the carriers being confined in a certain direction [1, 2]. These nanostructures are suitable for application of light emitting diodes, solar cells, PDs and so on. Surface modification of ZnO with narrow bandgap materials such as ZnSe, CdS, ZnS has been recognized as an efficient technique to improve the electro-optical prop- erties of ZnO [3]. Recent efforts highlight the usefulness of QD sensitized semiconductors in improving the photon-to- photocurrent conversion efficiency of the photoelectro- chemical cell [4]. The quantum confinement effect of nanocrystals (NCs) makes it possible to generate multiple electron–hole pairs per photon through impact ionization effect [4]. This work uses sensitized semiconductor layer to improve amount of absorption in UV region that is benefit to use in UV PDs. In this study, we used wet chemical approach for fab- rication of high density ZnO NP/ZnO NR arrays on ITO- glass substrates. 2 Experimental The fabrication procedure of ZnO NRs consists of two steps: preparation of seed-layer and growth of NR arrays. In the first step, solution of seed layer was prepared by dissolving 0.4 M zinc acetate dehydrate (Zn (CH 3 COO) 2 2H 2 O) and 0.4 M ethanolamine (NH 2 CH 2 CH 2 OH) in 2-methoxyetha- nol (CH 3 OCH 2 CH 2 OH). The resulting mixture was stirred using a magnetic stirrer at 60 °C for 30 min to get a clear and stable solution. The prepared solution was spin coated on the ITO-glass substrates at 3,000 rpm for 1 min. Then, the samples were dried and annealed in air at 450 °C for 1 h. In the second step, the substrates were placed in a heated solution (0.005 M) of zinc nitrate and (0.1 M) NaOH. This solution held at 70° C for 5 h. Finally, the samples were Z. Alaie (&)  S. Mohammad Nejad Nanoptronics Research Center, Iran University of Science and Technology, Tehran, Iran e-mail: alaie.zahra@yahoo.com; Alaie_zahra@iust.ac.ir M. H. Yousefi Nanolab, Malke Ashtar University of Technology, Esfahan, Iran 123 J Mater Sci: Mater Electron (2014) 25:852–856 DOI 10.1007/s10854-013-1656-6